No Difference in Reoperations at 2 Years Between Ceramic-on-metal and Metal-on-metal THA: A Randomized Trial
No Difference in Reoperations at 2 Years Between Ceramic-on- metal and Metal-on-metal THA: A Randomized Trial
C. Anderson Engh Jr 0 1 2
Supatra Sritulanondha 0 1 2
Abigail Korczak RN 0 1 2
Terrence David Whalen BS 0 1 2
Douglas D. R. Naudie 0 1 2
Richard W. McCalden 0 1 2
Steven J. MacDonald 0 1 2
MoM THA? 0 1 2
0 T. D. Whalen DePuy Synthes , Warsaw, IN , USA
1 A. Korczak , D. D. R. Naudie, R. W. McCalden, S. J. MacDonald Division of Orthopaedic Surgery, London Health Sciences Centre-University Hospital , London, ON , Canada
2 C. A. Engh Jr (&), S. Sritulanondha Anderson Orthopaedic Research Institute , 2501 Parker's Lane, Suite 200, Alexandria, VA 22306 , USA
Background bearings for total hip patient demographics between the study groups. Mean arthroplasty continue to warrant analysis even though followup was 50 months (range, 22-75 months). Seventycrosslinked polyethylene is performing very well. Ceramicon-metal (CoM) has low in vitro wear and did well in an two patients from two centers had metal level analysis. Results With the numbers available, there was no difearly clinical trial. We report on a prospective, randomized, ference in the proportion of patients undergoing revisions multicenter investigational device trial comparing CoM between the MoM and the CoM cohorts (MOM: 3% [six of with metal-on-metal (MoM).
This research project was funded (CAE, SJM) through a research
grant from DePuy, a Johnson & Johnson Company (Warsaw, IN,
USA). One of the authors certifies that he (CAE), or a member of his
or her immediate family, has or may receive payments or benefits,
during the study period, an amount more than USD 1,000,001, from
DePuy (Warsaw, IN, USA). One of the authors certifies that he (SJM),
or a member of his or her immediate family, has or may receive
payments or benefits, during the study period, an amount of more than
USD 1,000,001, from DePuy. One author (TDW) is an employee of
DePuy. The institution of one or more authors (CAE, DDRN, RWM,
SJM) has received funding from DePuy for the study. One or more
authors (CAE, SJM) has received personal fees from DePuy outside
the submitted work. One author (DDRN) has received institutional or
personal fees from Smith & Nephew (Memphis, TN, USA), Stryker
(Warsaw, IN, USA), Pfizer (New York, NY, USA), Zimmer (Warsaw,
IN, USA), and Exactech (Gainesville, FL, USA) outside the submitted
All ICMJE Conflict of Interest Forms for authors and Clinical
Orthopaedics and Related Research1 editors and board members are
on file with the publication and can be viewed on request.
Clinical Orthopaedics and Related Research1 neither advocates nor
endorses the use of any treatment, drug, or device. Readers are
encouraged to always seek additional information, including
FDAapproval status, of any drug or device prior to clinical use.
Each author certifies that his or her institution approved the human
protocol for this investigation, that all investigations were conducted
in conformity with ethical principles of research, and that informed
consent for participation in the study was obtained.
This work was performed at Anderson Orthopaedic Research
Institute, Alexandria, VA, USA, and London Health Sciences
Centre—University Hospital, London, Ontario, Canada.
erythrocyte and serum cobalt from 1 to 5 years (CoM
erythrocyte 0.45–0.55 ppb, p = 0.11 and CoM serum
0.88–0.85, p = 0.55, and MoM erythrocyte 0.32–0.51 ppb,
p \ 0.01 and MoM serum 0.65–1.01 ppb, p \ 0.01). In
addition, the MoM cobalt levels in erythrocytes and serum
at 5 years were more variable than at 1 year (erythrocyte
interquartile range [IQR], 0.26–0.44 to 0.31–1.21 ppb and
serum IQR, 0.42–0.80 to 0.64–2.20 ppb, p\0.02 for both).
Conclusions Although both bearings performed well at
short-term followup, the CoM bearing group had no
wearrelated revisions and maintained consistently low metal
levels. The MoM cobalt elevations may be important
considering recent reports of taper corrosion. This CoM
bearing was approved by the FDA but withdrawn from the
market because of low sales. If it were available, the
authors would not use CoM until long-term data were
available. The bearing would have to outperform
crosslinked polyethylene because it is unlikely that CoM metal
levels will return to normal.
Level of Evidence Level I, therapeutic study.
An ideal hip bearing surface would have qualities that
include low wear with biologically friendly wear debris,
allow larger head diameters, and be forgiving of
component orientation. Crosslinked polyethylene is the current
standard. However, head size is limited based on
recommendations of minimum polyethylene thickness of 4 to
8 mm. In addition, there is some concern about long-term
in vivo oxidation with degraded wear performance in the
second decade [
]. Ceramic-on-ceramic (CoC) has the
advantage of very low wear and comparatively friendly
wear debris. However, ceramic head size is limited by the
required liner thickness to avoid liner fracture. Most studies
have reported instances of insertional liner fracture or
squeaking, which also have limited CoC’s popularity [
]. Metal-on-metal (MoM) bearings became very popular
because of the large head sizes available and the potential
to greatly reduce dislocation. However, the debris
generated has caused local tissue reactions in some patients
leading to revision. For this reason large-head MoM
bearing use is less common. A final concern associated
with hip bearing surfaces is corrosion debris generated at
the stem-ball taper. This debris has led to local tissue
reactions requiring revision [
]. Although the evidence is
limited, the taper junctions with corrosion and local tissue
reactions appear to be more common when cobalt is
present at the taper junction.
A ceramic-on-metal (CoM) bearing for THA has been
studied in hip simulators and clinically at 12 months [
4, 5, 8, 10, 11, 19–23
]. The CoM bearing has potential
advantages over other bearing surfaces. The metal insert
can be thin allowing for 36-mm heads in metal acetabular
shells as small as 52 mm. A final benefit of this bearing
surface is the ceramic head interface with the femoral stem.
Retrieval studies have demonstrated lower corrosion at the
Morse taper when ceramic heads were used compared with
metal heads . The primary concern with a CoM bearing
is the metal debris generated at the bearing surface and the
potential biologic response. A prospective, multicenter,
randomized clinical investigation comparing the CoM
bearing surface with a MoM bearing was conducted under
an FDA-approved Investigational Device Exemption
(IDE). The results of this study have been submitted to the
FDA but have not been published (FDA, 2009; DePuy
Orthopaedics Inc IFU-78004780; DePuy Orthopaedics Inc
SSED; DePuy Orthopaedics Inc 2006; DePuy Orthopaedics
Inc PMA). This study reports the continued followup with
a mean followup of 50 months (range, 22–75 months) for
the 390 patients enrolled.
We asked the following questions: (1) Is there a
difference in the number or type of revisions comparing CoM
with MoM? (2) Are cobalt and chromium metal levels
different for CoM and MoM THA?
Patients and Methods
We designed a multicenter prospective randomized blinded
trial to compare CoM with MoM bearings using a variety
of uncemented femoral stems and a titanium acetabular
component. Between August 1, 2005, and October 31,
2006, 1015 patients from 11 centers were screened based
on inclusion and exclusion criterion. Inclusion criteria
included patients between the ages of 20 and 75 years with
noninflammatory arthritis. Exclusion criteria included
metal allergy, bilateral disease expected to require
contralateral surgery in 2 years, and known cancer. Patients
with a contralateral total hip were permitted as long as pain
in that hip was mild or less. Three hundred ninety patients
were enrolled. A block randomization with blocks of
random size was provided by the sponsor. Investigators or
designated research staff removed the next sequentially
numbered sticker to reveal the treatment group. Subjects
were blinded to their treatment.
All femoral and acetabular components were
cementless. The same titanium acetabular shell and metal liner
were used in all patients. The shell is porous-coated
titanium with a 10 self-locking taper for the metal bearing
surface (Pinnacle; DePuy, J&J, Warsaw, IN, USA). The
inserted metal bearing surface is high carbon wrought
cobalt chromium molybdenum alloy. Both 36-mm and
28-mm inner diameters were used, although only 11 of 194
of the ceramic and 13 of 196 metal femoral heads were
28 mm in diameter. Twenty-eight-millimeter heads were
used when the acetabular shell was smaller than 52 mm
because a smaller size shell did not accommodate a 36-mm
head size. The MoM metal femoral heads were high carbon
wrought cobalt chromium molybdenum alloy. The CoM
ball was a Biolox Delta ceramic (CeramTec AG,
Plochingen, Germany). Femoral stems were
surgeonspecific (each surgeon used one type of stem) and subject
to the randomization resulting in even distribution of stems.
The femoral stems used at the sites included a
cobaltchromium, extensively porous-coated, cylindrical (AML or
Prodigy; DePuy, J&J) in 94 hips (48 in the MoM group, 46
in the CoM group), a titanium proximally porous-coated
dual taper (Summit; DePuy, J&J) in 202 hips (101 in the
MoM group, 101 in the CoM group), and a titanium
proximally coated modular (SROM; DePuy, J&J) in 94
hips (47 in the MoM group, 47 in the CoM group). The
modular SROM stem has a 11/13 taper and all other stems
are a 12/14 taper for the stem-ball junction. The surgical
approach was also surgeon-specific; there were 265 lateral
approaches (131 in the CoM group and 134 in the MoM
group) and 125 posterior approaches (63 in the CoM group
and 62 in the MoM group). There were no preoperative
differences between the two groups in terms of age, sex,
body mass index, diagnosis or Harris hip score (HHS)
A subset of the 390 patients included 72 consecutive
patients from two centers who agreed to have metal level
analysis. The centers were chosen because they had
experience performing metal levels (Anderson Clinic and
London Ontario, the senior author sites). The patients
undergoing metal level analysis were a subset of the entire
cohort. Screening and randomization were not different
resulting in an equal number of patients in each study
group (36 CoM and 36 MoM). The only difference in the
patients undergoing metal level analysis was that one site
used a cobalt chromium stem (AML or Prodigy) and the
other site used a titanium stem (Summit). Blood samples
were collected preoperatively and at 12-, 24-, and
60-month intervals after surgery for analysis of serum and
erythrocyte cobalt and chromium metal levels. All
collection tubes and containers were determined to be free of
trace metal, and care was taken to prevent metal
contamination from the needle or collection tubes. Three 7-mL
Sherwood Monoject tubes (Sherwood David and Geck,
Markham, Ontario, Canada) of blood were drawn using
21gauge stainless steel needles. The first sample was
discarded, the second vial was processed for red blood cell
(RBC) evaluation, and the third vial processed for serum
analysis. All blood samples were processed within 30
minutes and then transported to the Trace Element
Laboratory at London Health Sciences Centre, London, Ontario,
Canada. All serum and RBC samples were analyzed by
high-resolution inductively coupled-mass spectrometry.
The instrument detection limits are less than 1.0 ppb.
Practical RBC detection limits are 0.05 ppb.
Clinical followup with HHS was done by the operating
surgeon at each site at 4 weeks, 3 months, and annually.
Radiographic evaluation was performed by a single
reviewer for the same intervals excluding 3 months. Stable
stems had less than 2 mm migration. Acetabular stability
required less than 2 mm migration and less than 4 change
in inclination. Femoral or acetabular radiolucencies
involving more than 50% of the implant surface were
considered a sign of failure. Osteolytic lesions greater than
5 mm in the largest dimension were reported.
Ninety-five percent (369 of 390) of patients had
minimum 2-year followup with a mean 50-month followup
(Fig. 1). In the cohort of patients who had metal levels
performed, 88% (63 of 72) had minimum 2-year metal
levels and the mean followup is 52 months (Fig. 2). Two
patients dropped out of the metal analysis group before
2 years because they had a contralateral MoM hip
arthroplasty, which could have altered their levels after the
index procedure but they were still followed in the larger
The study was designed to show noninferiority (NI) of a
success rate where success was defined as a composite of
HHS, radiographic, and survivorship outcomes. An 8% NI
delta was used, and from previous IDE study G960262, the
Ultima1 MOM Total Hip System (DePuy, J&J), success
rates were anticipated to be 93% in both groups [
power calculation indicated that sample sizes of 126 in
each group would provide 80% power to demonstrate NI
with a one-sided type 1 error rate of 5%. Sample sizes were
increased to 196 in each group to account for loss to
followup. Although a composite of HHS, radiographic, and
survivorship outcomes was chosen for the study design, the
authors have chosen to present revision and metal level
data as the primary manuscript questions. A
KolgomorovSmirnov test was used to evaluate the normality of
continuous data and Levene’s test for homogeneity of variance
was used to check for differences in variance. For
nonparametric data, a Mann-Whitney U test was used to test
for differences among two independent groups, a Wilcoxon
1 Incomplete Data
5 Lost to Followup 11 Total = 21 = 390
signed-rank test was used for related variables, and
Spearman’s test was used to evaluate correlations. Fisher’s
exact test and the chi-square test were used to examine
differences among categorical variables.
There were six MoM revisions (six of 196 [3%]) and three
CoM revisions (three of 194 [1.5%]) (odds ratio, 0.50; 95%
confidence interval [CI], 0.12–2.0; p = 0.33). The three
CoM revisions included a hematoma evacuation at 2
weeks, an infection at 23 months, and excision of
heterotopic ossification at 33 months. In the MoM group there
were four revisions unrelated to the bearing surface and
two bearing surface revisions. The four include a
hematoma evacuation at 7 days, recurrent dislocation at 4
months, infection at 19 months, and a broken femoral
component at 44 months. The first MoM revision attributed
to the bearing surface was revised 44 months after surgery
for an adverse local tissue reaction. This patient had pain
Followup at 2 Years or Greater Than
2 Years 369/390 = 95% Mean Followup = 50 Months Range = 22-75 Months
and elevations of erythrocyte sedimentation rate and
C-reactive protein. Preoperative hip aspiration revealed a
culture-negative purulent material. The patient underwent a
ball and liner exchange to a metal-on-polyethylene bearing
surface. The second MoM revision attributed to the bearing
surface occurred at 61 months. The patient developed hip
squeaking associated with a serum chromium of 81 ppb
and serum cobalt of 204 ppb. The cup inclination was
measured at 45 to 48 . This patient also had a bearing
exchange to a metal-on-polyethylene surface. The 5-year
survivorships free of revision are 98% (CI, 96%–100%)
and 97% (CI, 94%–100%) for the CoM and MoM groups,
respectively (p = 0.30). We report implant radiographic
data to address concerns about impending revisions. There
are no hips with loose femoral or acetabular components
and no acetabular osteolysis. Two patients in the MoM
group and one patient in the CoM group have small
femoral osteolytic lesions.
The metal level analysis revealed that CoM and MoM
metal levels were not different at 5 years of followup (p
values from 0.35 to 0.72) (Table 2). The only exception to
Laboratory Portion of Study
1 Contralateral MoM
1 Lost to Followup
1 Incomplete Data
this was the 5-year erythrocyte chromium comparison in
which the MoM level (0.56 ppb; interquartile range [IQR],
0.34–0.99) was lower than the CoM (0.92 ppb; IQR,
0.77–1.36) (p = 0.02). This isolated difference between the
two groups at 5 years is not important because the CoM
and MoM 5-year erythrocyte chromium levels were in the
normal range and did not increase from the preoperative
values (CoM 0.98 to 0.92 ppb, p = 0.39 and MoM 0.85 to
0.56 ppb, p = 0.17) (Fig. 3). A difference existed analyzing
the change within the CoM and MoM cobalt data from 1 to
5 years after surgery. The CoM erythrocyte and serum
cobalt levels did not increase from 1 to 5 years (erythrocyte
0.45 to 0.55 ppb, p = 0.11 and serum 0.88 to 0.85, p =
0.55). In contrast, the MoM erythrocyte and serum cobalt
increased from 1 to 5 years (erythrocyte 0.32 to 0.51 ppb, p
\ 0.01 and serum 0.65 to 1.01 ppb, p \ 0.01). The final
difference between the CoM and MoM groups was seen
comparing the cobalt data variability from 1 to 5 years. The
CoM erythrocyte and serum cobalt metal level variability
did not change (erythrocyte IQR, 0.28–0.83 to 0.38–0.69
ppb, p = 0.39 and serum IQR, 0.54–1.49 to 0.73–1.00 ppb,
p = 0.60). In contrast, the MoM erythrocyte and serum
cobalt values became more variable going from 1 to 5 years
(erythrocyte IQR, 0.26–0.44 to 0.31–1.21 ppb, p = 0.01 and
serum IQR, 0.42–0.80 to 0.64–2.20 ppb, p \ 0.01). The
increasing MoM cobalt metal level variance can be seen
visually as the increasing size of the MoM IQR (box plots)
from 1 to 5 years (Fig. 4). There was no correlation
between any metal level and cup inclination (CoM
erythrocyte and serum cobalt p = 0.84 and 0.77, CoM
erythrocyte and serum chromium p = 0.50 and 0.54, MoM
erythrocyte and serum cobalt p = 0.90 and 0.53, MoM
erythrocyte and serum chromium p = 0.34 and 0.77). The
mean cup inclination for the patients that had metal levels
was 46 ± 8 and 46 ± 8 for the CoM and MoM groups,
respectively (p = 0.89).
THA can be compromised by wear and the body’s reaction
to resulting debris. An ideal hip bearing surface would be
characterized by low wear with biologically friendly wear
debris, a variety of available head diameters, and tolerance
Medians are reported with the interquartile range. The Mann-Whitney test was used to test for differences between groups. The Wilcoxon
signedrank test was used for related variables. Levene’s test for homogeneity of variance was used to check for differences in variance. The reference
ranges for erythrocyte cobalt and serum cobalt are 0.02–0.29 ppb and 0.03–0.40 ppb, respectively. The reference ranges for erythrocyte
chromium and serum chromium are 0.04–0.64 ppb and 0.10–0.20 ppb, respectively; CoM = ceramic-on-metal; MoM = metal-on-metal.
to variation in terms of component orientation. CoM
bearings seem to offer some potential advantages. Hip
simulator studies have demonstrated low wear comparable
to CoC simulator wear, even in adverse conditions. The use
of CoM would provide the advantages of low wear with the
ability to use large femoral heads. CoM has been compared
with MoM in two randomized trials but the followup was
just 1 year [
]. We therefore compared CoM with
MoM bearings at mean 50-month (range, 22–75 months)
followup in a prospective randomized multicenter study
with the following questions: (1) Is there a difference in the
number or type of revisions comparing CoM with MoM?
(2) Are cobalt and chromium metal levels different for
CoM and MoM THA?
A weakness of the study is the choice of MoM as the
control bearing. In hindsight crosslinked polyethylene
would have been a better control device. The study was
designed and approved by the FDA before enrollment.
Enrollment occurred from 2005 to 2006. During those
years, MoM was a very popular bearing couple and 5-year
data on crosslinked polyethylene were not yet available.
Another weakness is the loss of 12 patients at the 2-year
followup. Although this is less than 5% of the study
population, it is possible that one or two additional revisions in
these patients could influence the revision comparison of
the two bearing surfaces. The use of more than one stem
allowing for different material combinations and taper
geometry is a concern. However, each surgeon used a
single stem design and followed the randomization
resulting in an equal number of a particular stem type in the two
study groups. At the two centers that measured metal
levels, the stems were different; however, comparisons of
metal levels from the two sites were not different.
Concerning metal levels, a reporting of acetabular anteversion
would have been a good addition to the inclination data
because increased wear from anterior or posterior edge
loading associated with poor anteversion might influence
metal levels. Lastly, we acknowledge that revision alone is
a blunt measure of success.
In our comparison of MoM with CoM, revision rates
were not different. There were six MoM revisions (3% [six
of 196]) compared with three CoM revisions (1.5% [three
of 194]). Although this seems like a small number of
revisions, it is not much different from registry data. The
2014 Australian and UK Pinnacle MoM 3-year revision
rates are 3% and 2.4% [
]. The 2014 UK also reports a
2.7% 3-year Pinnacle CoM revision rate. However, it is
important to note that both the Australian and UK
registries’ 5-year Pinnacle MoM revision rates increase to
4.8% and 5%, respectively. Currently MoM revisions for
reasons related to adverse reactions to metal debris are not
uncommon and modular, large-head MoM THAs have
fallen into disuse. In this study there were two
bearingrelated revisions in the MoM group and none in the CoM
group. One patient with MoM presented with squeaking
and very high metal levels, whereas the other had pain,
culture-negative purulent-appearing joint fluid, and was
revised for an adverse reaction to the MoM bearing. We are
aware of two other studies comparing CoM with MoM [
]. These studies focused on metal levels and only had
12-month followup. One of the studies reported CoM
revisions unrelated to the bearing surface for infection and
periprosthetic fracture [
]. With time we can expect more
bearing-related revisions in the MoM group and will need
to monitor the CoM bearings for the same type of failure. If
existing simulator data are predictive of clinical function
and patient outcome, the possibility exists that CoM
bearings will have lower revision rates.
At 5 years the median cobalt and chromium levels were
not different comparing the CoM with the MoM bearing.
However, this does not mean there were no differences.
The finding that MoM cobalt levels increased and became
more variable over time may have implications for future
MoM failures. This trend was not seen in the CoM group.
Current research indicates that MoM failures can occur
with or without bearing surface wear and that trunnion
corrosion is a cause of failure in some hips [
]. This is
interesting in light of our metal level trends. Bearing
surface failures in patients may be associated with the
comparatively higher simulator wear for MoM compared
with CoM. In addition, increased metal debris can originate
at the ball-stem taper junction secondary to corrosion. One
clinical study of metal-on-polyethylene failure has
identified a tendency for cobalt levels to increase preferentially
to chromium levels when corrosion is a cause of failure .
Another study has demonstrated that corrosion is lower
with a ceramic to metal taper junction than a metal to metal
taper junction [
]. We speculate that lower bearing
surface wear and less corrosion may contribute to the stable
and comparatively low variability of the CoM cobalt
levels. We are aware of two studies that compared CoM
with MoM metal levels. One study reported lower
12month CoM chromium but not cobalt levels compared with
]. The other study found no difference comparing
CoM with MoM metal levels at 6 or 12 months [
Neither of these studies had long enough followup to
recognize the 2- to 5-year MoM and CoM trends that we
report. Still it is important to remember that postoperative
CoM metal levels were elevated compared with the
preoperative state. The finding that both CoM and MoM
erythrocyte chromium remained at normal levels is
important, because it implies that the more toxic
hexavalent chromium is not being absorbed.
At a mean followup of 50 months, there was no
difference comparing the MoM with CoM revision rate
or the comparison of MoM with CoM median metal
levels in the subset that had metal levels performed.
However, the bearing related revisions and increasing
cobalt levels for the MoM group will likely contribute to
higher future MoM revisions. It remains to be answered
if the elevated but stable CoM metal levels will continue
and if revisions related to the bearing surface will also
remain low. Assuming good future CoM performance,
the bearing will have to be compared with crosslinked
polyethylene, which is the most common bearing surface
today. The CoM bearing described in this study was
approved by the FDA but withdrawn from the market
because of low sales. If it were available, the authors
would not use CoM until long-term data were available.
The bearing would have to outperform crosslinked
polyethylene because it is unlikely that CoM metal levels
will return to normal.
Acknowledgments We thank Robert Schneider MD, who
performed the radiographic review for the study.
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